It is known to provide WDM optical communications networks in the form of rings or interconnected rings. Typically these are bidirectional rings using two or four fibers. Various automatic protection switching schemes are known. For example, in a BLSR protection scheme, in the event of a fault, wavelengths travelling in one direction around the ring are switched to another fiber to enable them to reverse direction around the ring to reach their destination node. Traffic can be passed from one ring to another via electrical interfaces, or by optical interfaces having fixed preconfigured wavelength selections or by full featured reconfigurable optical switches with fault monitoring and protection switching capability.
It is known to use WDM optical networks for use in mobile backhaul networks. Current solutions for mobile backhaul networks may use L2/L3 switching with OEO (Optical-Electrical-Optical) conversion or microwave radio connections. The introduction of differentiated broadband services requiring low latency, the increase of the traffic load, the convergence of the mobile and fixed infrastructures, the need for sites consolidation and energy saving are all motivating the introduction of optical solutions in radio access and backhaul networks. This means packet processing is moved to the access and metro edge of the network and intermediate channel add-drop and ring interconnection is performed at the physical layer in the optical domain. Optical connections can help in saving energy, e.g. replacing switches for ring interconnection with ROADM based nodes or avoiding bridge sites. This is particularly so where protection is provided, in H-RAN parts for example. This implies equipment duplication.
As radio access networks (RAN) are evolving, the accompanying backhaul technologies are also being adapted constantly to meet the required cost-performance curve. The evolution in the RAN backhaul is today meeting the proven advantages of using optics in simplifying the network layer: transparency, availability of new low cost components and integrated systems, infrastructure scalability by easy increasing of number of channels and bit rates on the same network, long distance reaches facilitating site consolidation/convergence and low latency.
However the RAN access points (i.e. antenna towers and small cells) are geographically sparse: complex topologies are needed to pick-up the mobile traffic where it is. The DWDM technology is the ideal solution, natively providing a multi-channel transport (the “wavelength comb”). However a combination of DWDM rings and trees shall be considered to cover all the backhaul area. Network operators are straining to meet the stringent latency and increased capacity requirements of LTE and to be prepared to the next step: the 5th Generation (5G) communications network. For modernizing mobile backhaul solutions, such as evolving from SONET/SDH or ATM backhaul to packet, it's required to have a physical layer able to provide big and scalable pipes from the client side to the service edge. Optical technology has advantages for this, being natively broadband, scalable, and transparent. However it is perceived as costly and complex.